1. Field of the Invention
The present invention relates to a light emitting device that can be used as illumination apparatus, display, backlight for cell-phone, auxiliary light source for moving image illumination, and other light source and a method of manufacturing the same.
2. Description of the Related Art
Light emitting devices using light emitting element such as light emitting diodes are small in size and have good power efficiency, and can emit light of a bright color. Also, differing from such as electric light bulbs, such light emitting elements are free from burn out and the like. Further, they are excellent in initial drive performance and have excellent durability for vibrations and/or repeated ON/OFF operations. Owing to such excellent properties, light emitting devices using light emitting element such as light emitting diode (LED), laser diode (LD) and the like are utilized as light sources for illumination apparatus, back light for cell phone, and the like.
A protective element such as Zener diode may be mounted in such light emitting devices to protect the light emitting element from a damage caused by overvoltage. Such a protective element is disposed adjacent to a light emitting element on a supporting substrate where the light emitting element has been mounted, and is electrically connected to the light emitting element.
For example, the light emitting device disclosed in JP H11-54804A includes an insulating substrate having a first electrode and a second electrode of different polarity, an LED chip disposed on the upper surface side of the first electrode, a protective element (e.g., Zener diode) disposed on the second electrode, and a sealing resin covering the LED chip and an electrically conductive wire connected to the LED chip. Further, one electrode of the LED chip is connected to the first electrode and the other electrode of the LED is connected to the second electrode via a wire, respectively. On the other hand, the electrode of the upper surface side of the protective element is connected to the first electrode via an electrically conductive wire and the electrode of the lower surface of the protective element is connected to the second electrode via an electrically conductive adhesive.
In such case, a part of light from the light emitting element may be absorbed by the protective element and/or be intercepted by the protective element. Thus, the overall light extraction efficiency of the light emitting device may be decreased. Therefore, when a recess is formed under the protective element so that the height of the protective element is lower than that of the light emitting element, and the protective element is disposed in the recess, interception of light by the protective element can be decreased.
Alternatively, interception of the path of the light from the light emitting element to be extracted out of the light emitting device can also be prevented by disposing a reflecting member between the light emitting element and the protective element, other than the light transmissive member covering the light emitting element so as to reflect the light from the light emitting element toward out of the light emitting device, as described in JP 2007-150229A. In view of workability and the like in a case where a plurality of semiconductor light emitting elements are mounted on a supporting substrate, the recess for housing the protective element is preferably formed in the supporting substrate so that the opening of the recess is situated in the same plane as the plane where the light emitting elements to be mounted.
However, if the protective element is mounted in the recess formed lower than the mounting surface of the light emitting element, a part of light emitted from the end surface of the light emitting element which is located above is confined within the recess. As a result, light extraction efficiency of the light emitting device is decreased. Further, when the body color of the protective element is such that it absorbs the light from the light emitting element, the confined light is absorbed by the protective element and the output of the light emitting device is significantly reduced. Also, it is not practical that when the recess which houses the protective element is encapsulated with a reflective filler to prevent the light from entering the recess, additional time and material cost are required.
It is therefore an object of the present invention is to provide a light emitting device having excellent reliability and optical properties and to provide a method of manufacturing such light emitting device at a lower cost.